AbstractsEarth & Environmental Science

Underground construction of the Rio Piedras section of the Tren Urbano project involved the construction of twin tunnels (6.3m diameter) with Earth Pressure Balance machines in weathered alluvial soil. The depth of the cover over the tunnel crown varies from 13m to 10m. The twin tunnels, which connect the Rio Piedras Station and University of Puerto Rico Station, each have a length of 433 meters. Precast concrete linings offered the final structural support. Ground deformations were monitored throughout the construction of both twin tunnels. Volume loss is defined as the volume of ground loss as a proportion of the final tunnel volume and is measured in the plane perpendicular to the tunnel heading. Volume losses corresponding to the process of tunnel construction are identified in this thesis. Settlement troughs both over single and twin tunnels (when symmetric) are often described by a Gaussian curve. However, previous studies have suggested that the settlement trough due to twin tunnels is not symmetric with respect to the midpoint between the two tunnels. The current research shows that the superposition methods proposed by Suwansawat and Einstein (2007) are able to describe the observed settlement trough of the two bored tunnels with volume losses ranging from 0.9 to 1.8% for each bore. These results are up to a factor of 2 larger than volume losses predicted by empirical methods based on overload factors (Macklin, 1999).